The positioning control of semiconductor producing devices, machine tools, industrial robots or the like is frequently performed by using an electric motor. Since the positioning accuracy is greatly affected by the resonance frequencies of machines, precise resonance frequencies are desirably previously grasped. At the same time, the resonance frequencies are desirably precisely measured under a state tat a control system is attached and operated. Owing to this necessity, a method that frequency characteristics are analyzed by using a FFT to deduce the resonance frequency has been hitherto employed. The prior art is described by referring to the drawings.
FIG. 11 is a block diagram showing the structure of a prior resonance frequency detector attached to an electric motor control system. In the drawing, reference numeral 1 designates a command generator, 2 designates a controller, 3 designates an electric motor, 4 designates a machine, 5 designates a detector, 12 designates a FFT analyzer and 13 designates an output device. They operate in such a manner as described below.
The command generator 1 generates a command signal C of any of a sweep sine wave, a white noise wave, an M series wave form, an impact wave, etc. and supplies the command signal to the controller 2. When the controller 2 supplies electric current to the electric motor 3 in accordance with this command, the electric motor 3 drives the machine 4. At this time, the detector 5 detects the amount m of operation of the electric motor such as the rotating position or the rotating speed of the electric motor 3 to output a response signal S. When the command signal C and the response signal S are simultaneously inputted to the FFT analyzer 12, the FFT analyzer performs a FFT calculation and calculates frequency characteristics F. When the frequency characteristics F are inputted to the output device 13, the output device 13 outputs numeric values or graphs in visualized forms. In such a way, when a resonance frequency is measured, the resonance frequency affects the electric motor control system for stabilization.
The stabilized control system is described by referring to FIG. 12. In FIG. 12, reference numerals 2 to 5 respectively designate a controller, an electric motor, a machine and a detector the same as those of FIG. 11. Reference numeral 7 designates a closed-loop controller and 8 designates a filter processing part. The filter processing part 8 is provided to suppress the resonance frequency of this control system. The frequency thereof is set by manually inputting a filter part input value B corresponding to the measured resonance frequency. When the frequency is set as described above, a desired operation command M is supplied to allow the control system to perform a desired operation so that the machine 4 is driven by the electric motor 3.
However, according to the prior art, a calculation using a large quantity of data has been necessary to measure the resonance frequency by a FFT. Since a FFT analyzer which is not ordinarily used for controlling the electric motor needs to be separately prepared or an expensive computer which can performs a FFT calculation and a large quantity of calculation process is required, a calculation time has been disadvantageously increased, a cost has been increased, and further, a maneuverability has been not good.